The present invention pertains generally to digital electronics and specifically to a digital technique for dynamically modifying the individual pulses of a pulse train to conform to a predetermined duty cycle.
To assure the faithful transmission and reception of dial pulses used in telephone systems for identifying a called telephone number, stringent requirements are placed on the pulse train parameters. for example, the pulse rate is normally designed to lie within a range of 8-12 pulses per second (with each pulse representing a decimal value 1 and the number of pulses in a single pulse train representing the decimal numerical value for a particular digit of the called number) with a duty cycle of about 60% for each pulse. To meet these requirements in long distance calling, where the vagaries of the transmission medium may severely distort the dial pulses, it is common practice at tandem switching and repeater points to appropriately modify the received input pulse train before retransmitting it, particularly so as to meet the duty cycle requirement. Although there are many analog and semi-analog techniques such as disclosed in U.S. Pat. No. 3,637,943, entitled "Telephone Signaling Unit" for accomplishing this, the prior art does not teach any wholly digital implementation which capitalizes on the many well recognized benefits realized from a totally digitalized design. In this connection, it should be pointed out that although digital designs are eminently compatible with information storage and retrieval, the telephone system application herein requires a dynamic design wherein the modified output desired pulses are generated and transmitted as their counterpart input pulses are received. Thus, standard and wellknown digital storage techniques do not appertain.
With the foregoing in mind, it is a primary object of the present invention to provide a new and improved technique for dynamically generating an output pulse train from an input pulse train which conforms to a predetermined duty cycle within the cyclical period constraints of the input pulse train.
It is a further object of the present invention to provide such a new and improved technique which strictly employs digital elements.
It is still a further object of the present invention to provide such a technique which is well adapted for telephone system utilization.
The foregoing objects as well as others and the means by which they are achieved through the present invention may best be appreciated by referring to the Detailed Description of the Preferred Embodiment which follows hereinafter together with the appended drawings.